I really don't agree with this. I'm a 27 year old JS-focused web dev @150k base.
I understand that the bootcamps and proliferation of web-teaching schools have made web dev seem like the easy thing, and I agree that what I do is less complex than these $800k-earning data engineers, but web development in 2019 is no joke. The same goes for iOS/Android.
The types of things these companies are trying to build are not just "slap it together in a week and done" type projects and it takes experience to architect and engineer them effectively. Your average bootcamp grad is not able to do it yet.
iOS/Android/Web development forms the 3 primary portals to a company's clients, and as long as that's true, the value of such skillsets will remain high.